辐照处理血蜜蜡的颜色成因及鉴定特征研究

Study on Color Formation and Identification Characteristics of BloodAmber Produced by Irradiation

琥珀是一种价值较高的有机宝石,近年市场上普遍出现疑似经人工辐照而成的血蜜蜡。选取4块天然琥珀和1块柯巴树脂,通过电子束结合60Co辐射源,对其进行辐照改色。结果显示,经辐照处理后的天然琥珀和柯巴树脂呈现血蜜蜡的外观特征,出现亮丽的橙红或红色。采用超景深显微镜进行放大观察、紫外可见光光谱、红外光谱和电子顺磁共振对改色前后的样品进行系统研究。得出以下结论,辐照后的琥珀和柯巴树脂内部均产生树枝状闪电纹,这是绝缘体材料在电子束轰击下产生的一种闪电纹状放电通道。由于琥珀及柯巴树脂内部常存在凹陷、裂隙等位置,极易成为击穿放电的触发点,因此,当固体介质被击穿后,会在击穿路径留下放电痕迹。琥珀和柯巴树脂经过辐照后产生的树枝状放电结构无明显差异,均呈单独支脉状分布。红外光谱、紫外可见光谱对琥珀及柯巴树脂是否经过辐照处理不具有鉴定意义,改色前后样品的特征吸收峰无明显差异,表明其分子骨架未遭到严重破坏。电子顺磁共振结果显示,经辐照处理后的琥珀及柯巴树脂会导致其结构中某些烃基共价键均裂而形成带未成对电子的基团或原子团,即自由基。辐照时间越长,共振峰面积越大,表明产生的自由基的自旋浓度越高,颜色加深越明显。而辐照处理前的所有样品的共振峰面积几乎为0,表明天然琥珀及柯巴树脂内部的自由基的自旋浓度接近0。由此可以推断自由基的产生是导致其颜色变化的根本原因。电子顺磁共振测试通过刮取少量的粉末,直观地判定辐照产生的自由基自旋浓度与颜色的关系,为揭示血蜜蜡的致色机理提供依据。结合树枝状闪电纹的产生,可作为辐照处理血蜜蜡的鉴别特征。

Amber is a kind of organic gemstone with high value,and blood amber is a new kind of amber appearing in recent years,which is generally believed to be artificially irradiated.Four pieces of natural amber and one piece of copal resin were selected to be irradiated by an electron beam combined with a 60 Co radiation source to change their color.It indicates that the irradiated samples showed the appearance characteristics of blood amber,and the color is bright red.Magnification observation was used by a 3D microscope system.UV-Vis,FTIR,and electron paramagnetic resonance were used to systematically study the samples before and after color modification.It can draw the following conclusions.After irradiation,the dendritic lightning striations were formed in amber and copal resins,which is the lightning streak discharge channel produced by insulator material under electron beam bombardment.Because there are pits,cracks and other positions in amber and copal resins,it often becomes the trigger point of breakdown and discharge.Therefore,the discharge trace will be left when the solid medium is broken down.There is no difference in the dendritic lightning striations between amber and copal resins after irradiation,and they are distributed in a single branch.IR and UV-Vis spectra have no significance in identifying whether amber and copal resin have been irradiated.It is no difference in the characteristic absorption peaks of the samples before and after color modification,indicating that the molecular skeleton was not seriously damaged.Electron paramagnetic resonance(EPR)spectra reveal that the irradiated amber andcopal resins will lead to the splitting of covalent bonds of some hydrocarbon groups in their structure and the formation of atomic groups with unpaired electrons,which is the free radical.The longer the irradiation time,the larger the formant area,indicating the higher the spin concentration of free radicals and the more obvious the color deepened.The formant area of all samples before irradiation is almost zero,indicating the spin concentration of free radicals in natural amber and copal resin is close to zero.It can be inferred thatthe generation of free radicals is the fundamental cause of color change.Electron paramagnetic resonance testing can determine the relationship between the spin concentration of free radicals produced by irradiation and color by scraping the small amount of power.Combined with the generation of the dendritic lightning striations,it can be used as the distinguishing characteristic of blood amber produced by irradiation.